This invention relates to cleaning molds used in the glass fabrication industry in a cost effective and environmentally safe manner.
The glass industry utilizes glass molding equipment for the fabrication of glass containers and other articles. In the molding process, substantially pure primary graphite powder mixed with various proprietary chemical compounds is applied to the molds in order to facilitate mold separation and glass flow. The various proprietary chemical compounds function to disperse and bond the graphite to the molds. Because glass temperature during molding reaches about 2,000xc2x0 F., the chemical compounds react to cause a layer of substantially pure primary graphite to become chemically bonded to the molds. After successive applications of the graphite powder/chemical compound mixture as required by the glass process, a closely laminated layer of graphite containing trace amounts of proprietary bonding agent is built up on the mold. This graphite layer must then be cleaned from the mold when its thickness adversely affects the dimensional requirements of the glass container being produced. The characteristics of the bonded layer are that of graphite, in particular with a melting point of about 5,800xc2x0 F. and a boiling point of about 6,700xc2x0 F.
Due to the lubricating nature of the graphite, its removal has in the past been effected by abrasion using relatively high energy particles in a so-called blasting operation. This is effective but results in damage to the mold due to the inability to limit the particle trajectory solely within the boundary of the graphite layer. The result is damage to the mold which limits the mold life. The blasting operation can be moderated to minimize damage to the mold, but a proportionately longer time is then required to totally remove the graphite layer.
It is therefore an object of the present invention to provide an improved method for removing a graphite layer from a glass mold, and to provide apparatus for carrying out the method.
According to the present invention, a method of removing graphite from metal molds used in the glass fabrication industry includes placing a metal glass-fabricating mold with graphite bonded thereto in a chamber, providing an oxygen rich mixture of combustible gases in the chamber, with the oxygen rich mixture containing from about 10 to about 25% stoichiometric excess of oxygen, and igniting the oxygen rich mixture of combustible gases in the chamber to produce a temperature of at least about 6,000xc2x0 F. and a pressure wave. A high temperature wave front and the pressure wave thereby produced remove graphite from the metal mold by ablation of the graphite.
The invention also provides apparatus for removing graphite from metal molds used in the glass fabrication industry, the apparatus including a housing having a mold-receiving chamber, a gas supply for supplying an oxygen rich mixture of combustible gases to the mold, receiving chamber, with the oxygen rich mixture containing from about 10 to about 25% stoichiometric excess of oxygen, and an igniter for igniting the oxygen rich mixture combustible gases in the chamber to produce a temperature of at least about 6,000xc2x0 F. and a pressure wave. A high temperature wave front and the pressure wave thereby produced, remove graphite from a metal mold in the chamber by ablation of the graphite. An exhaust valve is subsequently operable to remove products of combustion from the chamber.
The apparatus also includes a mold feeder carriage moving horizontally between an open position outside the chamber and an operative position inside the chamber, a chamber closure member moving with the carriage to close an open end of the chamber when the carriage is in the operative position, and a pair of wedge members movable between retracted and operative positions and which, in the operable positions, engage the closure member to retain it in the chamber-closing position.
The ablation step is believed to comprise melting and partial oxidation of the graphite and subsequent removal of brittle oxidic material so formed.